A magnetic disk drive includes a rotatory magnetic disk, and a magnetic head slider supported by a magnetic head support mechanism and capable of being positioned with respect to a direction parallel to a diameter of the magnetic disk. The magnetic head slider is moved relative to the magnetic disk in a plane above the magnetic disk to write/read magnetic information to/from the magnetic disk. The magnetic head slider is caused to fly over the magnetic disk by the wedge effect of an air film serving as a pneumatic bearing so that the magnetic head slider may not directly come into solid-contact with the magnetic disk. Increasing linear recording density by reducing the distance between the magnetic head slider and the magnetic disk, namely, the reduction of the flying height of the slider, is effective in enhancing the high-density recording capability of the magnetic disk drive, and increasing the capacity of the magnetic disk drive or reducing the size of the magnetic disk drive.
A designed flying height is determined allowing for a flying height reduction that may be caused by machining errors and variations of atmospheric pressure and temperature in the working environment. Thus a designed flying height includes a flying height margin to ensure that the magnetic head slider never comes into contact with the magnetic disk even under the worst condition. The flying height margin can be omitted, contact between the magnetic head slider and the magnetic disk can be prevented and the flying height of the write/read element can be greatly reduced if the magnetic head slider has a function to adjust flying height for each magnetic head according to the condition of the working environment.
A slider structure proposed in Japanese Unexamined Patent Publication No. 2005-135501 (“Patent document 1”) includes a heater held between a slider base and a read element to heat a part of a thin film head when necessary such that the thin film head undergoes thermal expansion and juts out to adjust the distance between a magnetic recording medium, and the read element and a write element. FIG. 12 is a sectional view of the thin film head of a magnetic head slider mentioned in Patent document 1. A heater 122 is disposed between a slider base 1a and a read element 2. FIG. 13 is a plan view of the heater 122. The heater 122 is formed by extending a thin heating line of a thin resistive film in a zigzag shape parallel to the slider base 1a. 
A slider structure proposed in Japanese Unexamined Patent Publication No. 2005-056447 (“Patent document 2”) includes a protruding part formed by surrounding a heater and a write/read element by a soft resin film.
High power consumption is a problem in a magnetic head slider capable of flying height adjustment. A magnetic disk drive to be incorporated into a portable device, in particular, is subject to a severe restriction on power consumption. Whereas a piezoelectric actuator and an electrostatic actuator do not consume power for maintaining a flying height, a thermal actuator using a heater needs power for adjusting the flying height of the slider while the magnetic disk drive is in operation. Therefore, the power consumption of the magnetic disk drive needs to be reduced through the development of a thermal actuator capable of efficiently converting power into the deformation (projection) of the protruding part.
A method of suppressing the conduction of heat generated by the heater to the slider base by forming a thick insulating film on the slider base, and a method of increasing the thermal deformation by surrounding the heater by a soft resin film as mentioned in Patent document 2, are effective in increasing the projection caused by heat generated by the heater.
However, the thick insulating film impedes the dissipation of heat generated by recording current to the slider base. Consequently, thermal protrusion caused by recording current increases. The thermal protrusion caused by recording current is a protrusion resulting from thermal expansion on the order of nanometers caused by heating parts around the write/read element of the head by the sum of heat (iron loss) generated in the magnetic pole by eddy current produced by electromagnetic induction caused by the recording current flowing through a coil, and heat (copper loss) generated by the recording current flowing through the coil. A designed flying height of the slider is determined allowing for a flying height reduction that may be caused by machining errors and variations of atmospheric pressure and temperature in the working environment and includes a flying height margin to ensure that the magnetic head slider never comes into contact with the magnetic disk even under the worst condition. Accordingly, the thermal protrusion attributable to the recording current must be reduced to the least possible extent. Therefore, the insulating film is formed in the thinnest possible design thickness to promote the dissipation of the heat generated by the recording current to the slider base. However, the thin insulating film facilitates the dissipation of heat generated by the heater to the slider base and reduces thermal protrusion caused by the heat generated by the heater. Consequently, power consumption necessary for flying height adjustment increases accordingly.
The method of forming the soft resin film around the heater facilitates the deformation of parts in the vicinity of the resin film. Therefore, the thermal projection caused by a thermal actuator increases and, at the same time, the thermal projection caused by the recording current and the environmental temperature increases. The thermal protrusion caused by the environmental temperature is attributable to difference in the coefficient of linear thermal expansion among metal and resin materials forming the magnetic shield of the write/read element and the magnetic poles, and ceramic materials forming other parts. The thermal protrusion is a local thermal protrusion on the order of nanometers caused by increase in the environmental temperature.
Therefore, there has been demand for a heating structure capable of increasing a thermal protrusion caused by a thermal actuator without increasing a thermal protrusion caused by the recording current and environmental temperature. If a thermal protrusion is increased simply by thermal deformation, the protrusion produces an additional air pressure which increases the flying height of the slider and hence stroke cannot be increased as much as desired. Therefore, it is desired that a sharpest possible thermal protrusion is formed.